<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<body>
    <input type="text" name="" id="">
    <button>发送</button>
    <script>
        var btn=document.querySelector('button');
        var time=3;//定义剩下的秒数
        var timer=null;
        btn.addEventListener('click',function(){
            {
               btn.disabled=true;
               timer= setInterval(function(){
                if(time==0){
            clearInterval(timer);
            btn.disabled=false;
            btn.innerHTML='发送';
            time=3;
           }else{btn.innerHTML='还剩下'+time+'s';
               time--;}
          },1000);
           }                     
        })
    </script>
</body>
</html>